1. Field of the Invention
The present invention relates to a buffer amplifier that amplifies, and sets the level of, an oscillation signal output from a voltage-controlled oscillator or the like, and also relates to an electronic circuit unit using the buffer amplifier.
2. Description of the Related Art
The circuit configuration of a buffer amplifier of the related art will now be described with reference to FIG. 4. An amplifying transistor 21 is biased so as to operate at a predetermined operating point as an amplifying device with the emitter thereof being grounded. The amplifying transistor 21 has a base connected to an input terminal 22 and has a collector to which power is fed from a power supply B through an inductance element 23. The collector is also connected to a resistance attenuator 25 through a coupling capacitor 24. The inductance element 23 for feeding power and the coupling capacitor 24 are selected so as to match the impedances between the amplifying transistor 21 side and the resistance attenuator 25 side.
The resistance attenuator 25 is formed as an L-shaped asymmetrical attenuator. The resistance attenuator 25 is not necessarily used for impedance transformation or impedance matching, but is intended primarily for level setting of a signal. The resistance attenuator 25 is connected to an output terminal 27 through a DC-blocking capacitor 26.
For example, a buffer amplifier having the above configuration is used for setting the level of an oscillation signal of a voltage-controlled regulator for use in portable telephones. In such a case, a user (the manufacturer of the portable telephones) mounts a buffer amplifier as described above on a printed circuit board (not shown) according to the level characteristic of an off-the-shelf voltage-controlled regulator.
Since the buffer amplifier described above uses two capacitors, i.e., a coupling capacitor and a DC-blocking capacitor, it results in higher cost, and is also difficult to miniaturize.
In addition, the buffer amplifier involves complexity since the user has to match the signal level thereof with that of a voltage-controlled oscillator or the like that serves as an input signal source.
Accordingly, it is an object of the present invention to provide a buffer amplifier that is reduced in size and in the number of elements.
Another object of the present invention is to provide an electronic circuit unit in which the buffer amplifier is concurrently used with a voltage-controlled oscillator, which serves as a signal source, such that a signal level is set to a predetermined value in advance.
To these ends, according to a first aspect of the present invention, there is provided a buffer amplifier. The buffer amplifier includes an amplifier, an inductance element to feed power to a terminal of the amplifier from a power supply, a resistance attenuator having an input end, an output end, and a ground end; and an output terminal connected to the resistance attenuator. The input end of the resistance attenuator is directly connected to the terminal of the amplifier, the ground end is connected to the power supply, and the output end of the resistance attenuator is connected to the output terminal through a coupling capacitor. This arrangement provides a circuit having a reduced number of elements.
The resistance attenuator may be formed of an L-shaped, a T-shaped, or a xcfx80-shaped asymmetrical circuit. This allows setting of a signal level with a minimum number of elements.
The amplifier may be a transistor and the terminal of the amplifier a collector of the transistor.
According to another aspect of the present invention, an electronic circuit unit is provided. The electronic circuit unit includes the buffer amplifier according to the first aspect of the present invention and a voltage-controlled oscillator. The buffer amplifier sets the level of an oscillation signal output from the voltage-controlled oscillator. This arrangement allows elimination of the complexity of the user having to match the signal levels.
In another aspect the buffer amplifier comprises an amplifier having a terminal, an inductance element connected between the terminal of the amplifier and a power supply, and a resistance attenuator connected between the terminal of the amplifier and an output terminal. Only a single capacitor is connected between the terminal of the amplifier and the output terminal.